Skeletal structures are formed of bones and adjoining structures. These skeletal structures may require artificial support or stabilization. For example, the human spine is composed of a column of thirty-three vertebrae and their adjoining structures. Most of the vertebrae are capable of individual movement and ensure the general movement of the spine: flexion, extension, axial rotation and lateral flexion. An intervertebral disc is positioned between opposing faces of adjacent vertebrae. Each of these vertebrae includes a vertebral body, and a vertebral arch that encloses an opening, called the vertebral foramen, through which the spinal cord and spinal nerves pass. The body of the spinal vertebra is connected to the arch by the pedicles—one on either side of the arch—, which form two short thick processes. Unfortunately, there are numerous diseases that deteriorate one or more portion of the vertebra. For example, osteoporosis, scoliosis, kyphosis, spondylolisthesis, tumors, as well as fractures or extreme shocks may leads to the deterioration of vertebrae. As a result vertebrae may collapse, nerves may be pinched causing enormous pain, or regular movement of the column may be limited. In these and other situations, surgical installation of various devices is designed to allow the person to resume a normal life.
One well-known device for spine stabilization procedures is the pedicle screw, which is threaded for engagement with bone. A pedicle screw is surgically installed posteriorly into and through a pedicle. Bone screws, like pedicle screws, are commonly used to fix adjacent bones or bone fragments with respect to each other. For example, bone screws are commonly used to help repair fractures in bone, to attach bone plates to bone, to fix adjacent vertebral bodies, or for stabilizing the spine. When the bone is diseased, for example due to osteoporosis, deteriorated, for example due to prior surgical procedure, or degenerated, securing the bone screw may be problematic. For instance, when a pedicle screw is used on osteoporotic patients, the lack of bone density makes it difficult to properly engage the bone screw threads within the pedicle resulting in a fragile connection between the pedicle screw and bone.
Technical Issues
If the threaded portion of the screws does not properly secure to the bone, the bone screw will loosen and pull out or break. This loosening can occur over time. Therefore one of the issues intended to be solved by this invention is to provide an anchor system with improved fixation to bone. The anchor of the present invention is first inserted into the bone and ensures fixation with respect to the bone. The bone screw is then inserted into the anchor and the anchor ensures fixation with respect to the bone screw. Therefore the bone screw is better secured when inserted in the anchor, and the anchor ensures an efficient fixation between the bone and the bone screw.
Most of the orthopedic device manufacturers are currently selling bone screws with various shapes, sizes or diameters. Therefore another issue to be solved by this invention is to provide a universal anchor compatible with most of the bone screws on the market.
As bone screws present threads, they can be removed by unscrewing once the bone has been stabilized. The removal of the bone screw is necessary to avoid leaving unnecessarily foreign body inside the human body. However anchors, and especially expandable anchors, present hollows and asperities, into which bone may grow, preventing the ability to remove the anchors. As bone screws may be removed, it is another issue of the present invention to achieve removable anchors.